1. Field of the Invention
The present invention relates to a filter and a manufacturing method therefor. More specifically, the present invention relates to a filter for which a compact structure can be achieved by suppressing occurrence of welding burrs and keeping a weld portion and a burr gutter to the minimum required, and a manufacturing method therefor.
2. Description of the Related Art
A filter is known in which a pair of case members made of synthetic resin are welded together by vibration welding, and a filter element is held between the pair of case members (see JP-UM-A-H05-29735 for example).
JP-UM-A-H05-29735 discloses that, as shown in FIG. 12, for example, a joining portion 102a is formed at a lower end rim of an upper case 102, and joining portions 103a and 104a facing the joining portion 102a of the upper case 102 are formed respectively at an upper end rim of a lower case 103 and an outer rim of a screen frame 104.
According to JP-UM-A-H05-29735, nevertheless, the joining portion 102a of the upper case 102 is vibration-welded to both the joining portion 103a of the lower case 103 and the joining portion 104a of the screen frame 104 at the same time. Accordingly, this requires a sufficient flat area to be secured on a contact area of the joining portion 102a of the upper case 102, and a space (burr gutter) r for welding burrs that occur in a relatively large amount during vibration welding to be provided at both sides of the joining portion 102a of the upper case 102. Furthermore, the space r and a weld portion w are normally disposed along the entire periphery of the filter, thus enlarging the size of the filter.